1. Field of the Invention
The present invention relates to wireless communications, and more specifically, to a data transmission method and apparatus.
2. Related Art
In LTE (long term evolution) release 12, intensive research is underway for better performance in light of capacity, transmission coverage, inter-cell coordination, and costs. For such better performance, LTE release 12 is in discussion for adopting various techniques such as small cell enhancement, macro cell enhancement, new carrier type or machine type communication in technical aspects.
The enhancement in capacity and transmission coverage which is targeted by LTE release 12 may be achieved by unification between LTE-WLAN (wireless local area network) and small cell enhancement based on inter-site carrier aggregation and macro cell enhancement. As the cell size decreases, there is a frequent shift between cells, thus leading to an increase in the amount of traffic signaled when a user equipment relocates. To address such issues, the small cell enhancement may be utilized to reduce signaling that is transmitted from the RAN (Radio Access Network) to the core network, thus optimizing the small cells.
The NCT (New Carrier Type) is a newly defined frame type that is different from legacy frame configuration. The NCT may be a carrier type optimized for small cells, but may be applicable to macro cells as well. The NCT may reduce overhead that occurs due to transmission of a CRS (cell-specific reference signal) and demodulate downlink link control channel based on a DM-RS (demodulation reference signal). The new definition of NCT may save base stations energy consumption while reducing interference that occurs in the HetNet (heterogeneous network). Further, use of the NCT may decrease reference signal overhead that occurs when data transmission is performed using a plurality of downlink antennas. More specifically, the NCT may be defined as a carrier that maintains the existing frame architecture (e.g., CP length, sub-frame structure, duplex mode) but differs in the structure of a reference signal actually transmitted, i.e., not backward compatible (to Rel-11 and below UEs).